Thermal conversion of hydrocarbons



Dec. 5, 1950 R. B. EwELL THERMAL CONVERSION oF HYDRocARBoNs Filed Jan. 3, 1948 ronoomclXlm 3.

bq his Aqchgvl.

Patented Dec. 5, 1956 rnnitlvinncolwlinslorr or HYDRocAltoNs Reba-t Bartlett Ewell, Berkeley, foali'fl-, assigner toA shell Development company,A san-Francisca Calif., a' corporation of Delaware Appliatitnlranary s, lsisgser-ilNo. isi

(cil lcsisr It is an object of the' 'present invention" to prol vide a method off treating a plurality of4 hydrocarbon oil fractions of differing boiling ranges, such as may be obtained from a crude oil or partially 4topped crude oil, wherein at least two of said hydrocarbon fractions, and selected-prod# ucts produced therefrom, are treated under conditions selected foreach oil to produce inotor'` fuel products, and intermediate products suitable for further conversion, to eirecta combined operation of highest eiiiciency and particularly with a .minimum requirement in apparatus.

It is a further object of the invention to provide an improved inethod for the conversion of reduced cltlded oil te lighter products including `gasoline of high antikn'ock properties.` n A still further Objectis to provide a` inethod wherein a heavy naphtlia and a relatively heavyhydrcarbon oil such as reduced crude are simultaneously treated incombinatlontoefect reforming of the naphtha to produce gasoline constituents of im.- proved quality andthe Cracking of the heavy oil to produce gasoline constituents of. high antiknock value as well as of intermediate products.

Another object of the invention is to provide a method of the above nature wherein inter- Y mediate cracked products thus formed, and which are intermediate in boiling range between the heavy naphtha and reduced crudaare themselves treated in combination with heavy naptha and/or with reduced crude to produce therefrom gasoline constituents of good quality.

Still another object is to treat a plurality of hydrocarbon oilfractions of differingv boiling ranges and differing in their refractoriness toward heat in a ina-nner so as to effect a deeper cracking of the heavier and more readily cracked fractioms)y while at the saine time avoiding appreciable coking of the ir'laterial.y rThe above-mentioned Objects will be better understood and other objects will become apparent from the following descriptonof the invention, taken together with the' accompanying drawing which is a" flow diagram of an apparatus and method for carrying out the present invention.

The present invention contemplates tire sepa= ration of crude petrcleumpll crcf a' partially toppedicrude oiliijitoa lplurality of fractions, iii*- olliding ai low `boiling action suoli as fullrangesltraight 'run gasollneor a! heavy'naphthaf, a Highbclllugresuual-fraction tar'euuceu c'rl'l'd) aan' rate @calate 1aionboll'ing higher than lline, sucl'li as sto oil fraction; separately subjecting trleicw boiling fraction and: themen boiling fraction to elevated "riciitiiis of ten'- lre lirss'llre toleieit cracking andyor i lngofthe boiling fraction topr'odilce he combined resulting producti isnthenY separated are nigh' boiling residue tvl'ileii cannet be iurtllr cracked' without substantial tiring ami it a vapnriza vfllaa' fraction :the raconte otrheaaffacti-ills fractionated `intoy a plurality of fiactic'rlsllicliitllng atralteigaslliie rratl of improved' value,4 a nigh tolling'` residual iraction is recycled` toth"cl'acking "zone for treatingk :the residualloil 'fraction anda cracked hydrocarbon fractionV ci" intermediatewboiling `range `between that ofA the heavy naphthaand residual voil fractions-produced first from `the feed oil, which intermediate fractionf. being a Acraolne'i `product, xis more refractory thanA the lstraigl'lt run inteiniediategstove oil) fraction of the first frag;- tionation-in Athe sanieboiling range arid maybe and isrecyclediin the systern toghe subjected to cracking in admiXture-Wwth the4N low.v boiling straight run fraction-l in the" reforming zone therefor.` d y l* l Y It' will-baseert thatby thekinethod described above, al ol` theportion.of` the higher `boiling (residual). `fraction from the hrst fractionation 'which atv any tiin raoliedtoJ p :rodllce` lower boiling matrial'maybe convertedto useful gasoline of improved-value or lio-lighterhydrocarbons, Vwithout the production as lnal product ofintermediate boiling materiai'kwliiclft l's'` of' te? bien `boiling `point toY be` utilized Aas gasoline. Whereas intermediate cracldprdlctsiar'e produced ih the process, they can be subjected to the svre cracking and reforming treatment in the same heating, cracking and reforming zone as the low boiling straight run fraction without cracking thereof to deleterious coke, because of the increased refractory character of this cracked intermediate (stove oil-boiling range) fraction over that of the equivalent (in boiling range) straight vrun stove oil fraction. This is true particularly since, in the process of the invention, this cracked fraction is substantially free of less refractory straight run material.

It is preferred to countercurrently contact the heavy (residual) oil from the first fractionation operation, prior to heat treatment thereof, with the vaporized products of the thermal conversion operations, in the lower section of the second fractionating zone, and to utilize .the bottoms product therefrom as feed oil to the cracking furnace for the heavier oil. In this manner any vaporizable heavy (residual) material which is produced as a result of the thermal treatments, .will be admixed with the i-lrst residual material and returned to the conversion operations without loss thereof. Furthermore, this countercurrent contacting serves as a heat exchange means to provide adequate refluxing in the lower section of the fractionating zone to effect complete condensation of the intermediate cracked fraction for separation and recycle thereof for further cracking and reforming.

An important feature of the present invention is the separation of the intermediate cracked oil 'fraction and combining it with the lower boiling straight run distillate fraction and subjecting the two fractions together to the same severe reform- .ing and cracking conditions.

A number of advantages is secured by the practice of the method of the present invention. Among them are the following more important and signicant ones:

.(1) The octane number of the heavier straight run gasoline fraction is materially increased in addition to the production of a large proportion vof a similar gasoline fraction made from cracking heavier oils.

(2) The temperature of the light oil heater may bemaintained at a high level and by carrying a larger quantity of sensible heat to the reaction chamber more severe cracking of the heavy oil stock is obtained without the coking of furnace tubes than could otherwise be obtained.` (3) By providing a reaction chamber (zone of reduced linear velocity, enlarged cross-section and of reduced conning surface per volume of reactants), wherein the high sensible heat of the lighter oil is utilized more completely to effect deeper heating and conversion of the heavier oil without deleterious coking, the time of subjecting the reactants` to conversion conditions may be materially and advantageously increased since 'increased linear velocity is not now required to sweep any coke formed from narrow confining and heat transfer tubes as is accomplished by the .prior method of passing a naphtha fraction Ythrough an elongated cracking zone of restricted cross-section while applying heat to said elongat- I:edzoneto subject the'naphtha to cracking conditions of temperature and pressure adequate for the purpose and introducing a heavy (residual) oil to the same elongated cracking zone intermediate the endsthereof into admixture with the naphtha after it has been subjected to substantial conversion therein wherebysaid residual Oil is raised to a cracking temperature to effect con- 'version thereof to lighter products duringv the y 4 passage of the admixed hydrocarbons through the remainder of the elongated cracking zone.

(4) As already indicated hereinbefore, the intermediate condensate cut separated from the vapors of the combined cracked product, which intermediate cut has too nigh a boiling range (40G-600 F., preferably 4.50-550o F.) may now be recracked in the light oil heater along with the lighter oil (heavy naphtha) feed thereto. This recycle stream, in the absence of any straight run stove oil (boiling range of 40G-600 F.), can receive the same high temperature treatments as the lighter straight run naphtha (30G-400 E), since the two materials are of similar refractoriness. This makes it possible to. utilize the same equipment for treating both fractions, thus making it possible advantageously to convert the intermediate cracked fraction to more valuable lighter hydrocarbons of high antiknock value without the outlay of any further capital for additional plant equipment.

(5) An yunusually high yield of C3, C4 and C5 olens is obtained because of the reforming operation, the heavy recycle cracking, and the more severe cracking of the heavy oil. These olens are increasingly valuable as feed stock for polymerization and alkylation operations as well as for a diversity of chemical manufacturing operations.

(6) The presence of light reforming products in the admixture which is fed to the flash chamber or evaporator for the purpose of separating the vapors from the heavy residue admixed therewith permits a more complete recovery of the vaporizable products for a given operation bottoms temperature. In other words, for a selected bottoms temperature, which in turn is determined by the thermal characteristics of the materials involved, a heavier residue may be produced, thus representing a smaller fraction of feed material which is withdrawn from the system as residual product. Y

Having described the invention in a general manner and having set forth advantages to be obtained from its practice, the invention will now be described in more detail with reference to the accompanying drawing, but it is to be understood that the invention is not to be limited by such reference, but is capable of other modifications which may be beyond the physical limitations of the particular apparatus indicated.

Crude oil or partially topped crude oil is introduced into the system through line i! provided with a pump l2. The crude oil may be heated by any suitable means, such as by heat @Xchange with hot gases or vapors produced in the system, or the oil may be preliminarily heated partially by such means and raised to the final temperatureV desired by passage through a coil located in the relatively cool part of a cracking furnace, or such coil may be separately heated, or the crude oil may be heated entirely by passage through such a heated coil. For purposes of illustration and without intending to limit the invention thereby a separate heater i-'i provided with a suitable heating coil to which line i t connects is indicated. ln heater It the crude oil or partially topped crude oil is heated to a distillation temperature which will depend on the extent of distillation desired and on the nature of the charge oil. Generally speaking, the oil may be heated to a temperature of 500 to 800 F. under a pressure of from atmospheric to lo() pounds per square inch gage (p. s. i. g). The heated oil is withdrawn from heater i4 through a line l5 which i; isa-'provided' withi a :valve |65 tot efle'zctfanyir desired reductionrinl; pressure.- `Line |5. connects with the lower portion offra crude1-flas-h and''fractionating column` ori'itower |112v wherein the separation'sof vaporsv and1 reduced crude issqeffected `Thevre-` ducedcnude descendszto. the bottom oitheitower` Hi and` theheating of` the crude-` oil under com ditions: maintained? in. tower- Iz'i isregulated to effect vaporization of the majority of.:v constituents.: b oiling "below ,550%650" @preferably -below 6,605" E.' lunder atmospheric pressure) ,where bythe` crude soil orl partially. topped `crudeoil which may hayezhadi an:original gravityA off25 to 45 `A. .P. I-.nis distilled .to leave areduced' vcrudehavinggazsgravity of 10,9 to 30Sif P'. I: Auxiliary heating meansf l 9. mayrbez-4 provided in the .bottom oftheutower' LIr to: secure thedesir-.eddistillation, if-rnecessary.

Conditions4 of. temperature.- and. `pressure-,are maintained: in tower L1 tu eiectA condensation. of a part of the vapors wherebythe vaporstleaving t'stoprconsst of, a imixturef` of: light. hydrocarbons. ForV example, l the.` towermay be maintained'` at a pressure from atmosphericf to. `Y poundsper square inch with. a. bottom. temperature `of v500" to; 6,570. E; andratcpftemperature of 275"` to 325 sure)- andia'virgin light gasoil- (stove oil) having,

for example, ai boiling' range of about: 400 to 600 F. Other `l`speciiic cuts ori fractions may be obtainedE if" desired? andv tound'to be more satisfactory depending on the nature of the'partieul'ar crude oil-or oili mixture being utilized forthe feed ohargein the operation of the--process Theioverheadvaporous products are withdrawn from the top` oftower lrlthrough' aline Zd; at least?partiallycondensed a suitable condenser 2T and collected in a suitablevessel 29; A portion of` the condensate'itl'iusr produced maybe returned through line 2U-to the top'- of tower "l1 as re-lux condensa-te While the remainder iswith- Vdrawn through Va line Uncondensed vapors or gaseous materials are vented-i or withdrawn through a line 3,!-1 The lightnaphtha (light gasoline) condensate' is `Withdrawn from trap-'out tray' 22 vvithintowersil through a line 32 and may be utilizedL assuch-` or, as light blending Amaterialfor ultimate consumption. The virgin light gasoil (stove oil')' condensateY which collects on trap-out tray" 25 is withdrawn from tower il through a line 34y and transferred te a storage vessel 35 from which it is-withdrawn4 through a valved line 36-as it is desired'. The heavy'naphtha condensateV is withdrawn; fromV trap-out tray 24 through line 3-11 provided with a valve 39', by means of pump di] located in line 31. Line 31 connects with the coil of `the reforming heater 4l`. ing heater 4l is shownA asa separate heater. It will" be understood that this `representation for purposes onlyof' illustration, however,` is not intended to limit the invention to` that particular arrangement. The function of heater ll'l7 maybe For convenience of` representation, reformreducedf crudefand heavyfrecycle. oil, that is heaterrk Ther heavy. naphthal is heated as it passesI through heater 4l' to af suitable reforming temperatureiof from about:900`i to 4:1 1100?"F:ata pressure v of llUOto-lOGO poundsiper-squarewinchto eilect cracking :ofTo the naphtha with `accompanying polymerization andflother conversion reactions to: eiiect the production of a` reformed: na-phtha having improved@ antiknock properties.` Simultaneously` with the heating of.; ther heavy naphtha in. heater# 411-, reduced crudesi'swithdrawn. from the bottom Vofftower.` lii't'throughiline 42; counter-v currently: contacted` asl Vwill be; described hereinafter withwvaporous: reformed and" cracked products, of ai prior `cracking land reforming op eration ofxthe processandithen: conducted to theV heating coil ofi a. suitable heater- 4'41; Thefheavy: oil-` (reduced crude)e is1heatedi in, the coil of vheat-f erll:V toatemperatureotffrom about 850 to 975 E; ata.pressureoitrom. about lOOftoi about 1(l'00`= pounds.- personare inch, a tempera-ture ofY the order -of "817519 to- 92592K ata4 pressure of the order ot250"=to450"p,s.isa. (pounds` per square inch absolutel representing a preferred combination of. operating conditions The reduced crude withdrawn from tower: l-'lisordinarily at a temperatureot'OU? tol '700915K The reduced' crudethus-r heated4 inA heater #442i `Wliereby at least a pantia'li cracking-of" the oilf `is eifected, however, the'y temperature tol `which the `cil is-heated inb heater =44= andi ther-period of time of residence oiithe `oilthereinare adiusted soas. to effect-a maximum of cracking and `conversion witheut thel forniti-tioni oi` coke therein.

The` heated andi crackedproducts i ffl-om heat ers-r Lll" and" 4-4 are withdrawn7 through lines yl5z and, respectively, `eachof which is `providedwith `suitable valves formaintaining optimum cracking' pressures in each coil, and the separate products thereiny are combined in line '4'7- (which--may be of negligible l'engtli and-` then.` delivered tofV a: -reactionchamber 49 of` -enlarged crossesectibny whereinV the linear velocity; of' the, admixture is materially decreased and the; hydrocarbon substances Vare" permitted to undergo furtherV conversions with the production of.' further amounts lof valuable lowerl molecular weight hydrocarbons. VEven ifA the conditionsv maintained in the heaters 41 and 44 are `such that;-when-the admixture of-*productsi reaches the reaction `chamber 49 there is then deeper crackingx oftheheavy' oil' ofsuch a degree as to i produce an appreciable amountv of coke, many of `the advantages of the linvention are still realized and the disadvantage of the coke formaltionl is `now readily obviated by the provision Aof a secondI reaction chamber' 49a in parallel. withl chamber 49 and which may be used alternately therewith, one chamber beingy de-ooked by burning out or'otherwise-removing' the coke whilethe other chamber isbn-stream. Alternate lines llc4 and 50a are provided for directing, the adrnixture through chamber 49a. Since the reaction chambers do not require the transfer of heat ythrough the, walls thereof and-since` they' are of erl lnrtheradmi'xture with the `heavy oilmakes itl possible to heat the heavy oil and its cracked products to a higher temperature, utilizing the additional sensible heat of the heavy naphtha reformed products, to elect a higher temperature with greater conversion of the heavy oil without coke formation therefrom in the reaction chamber 69. On the other hand, the present invention may be operated for the deliberate formation of cokeu in the chambers, with advantages being secured due to deeper cracking as a result of increased availability of sensible heat for the purpose. When the process is so operated, various suitable means, such as well known hydraulic or mechanical means, may be utilized for removing the coke from the chambers.

The cracked products from the reaction chamber are withdrawn therefrom through line 50 provided with a valve l to effect any desired reduction in pressure. The line 50-fconnects with a flash chamber separator 52, which, if it is desired may be provided with fractionating means therein such as a numberof bubble-cap plates. The separator 52 may be maintained at 0r below the pressure in the reaction chamber 49 and the heaters 4l and 54, but,v preferably the pressure is somewhat lower than that of the reaction chamber whereby separation of vapors and liquid residue is effected to produce vapors containing the desired constituents. The temperature of the constituents in the flash chamber 52 may be 700 to 850 F., preferably 775 to 825 F. If it is desired or necessary, a quenching oil may be introduced into the separator 52 at a point above the point of introduction of the cracked products by any suitable meansy (not shown), which quenching oil may be a portion of a higher boiling light fraction obtained by a subsequent fractionation of the cracked and vaporized products vand which may or may not contain absorbed therein some of the separated hydrocarbons of still lower molecular weight. The liquid residue separated in the ash chamber is withdrawn therefrom through a valved line 5d for use elsewhere, for example, as a fuel oil, road oil, etc. The vapors separated in ash chamber 52 are withdrawn therefrom through a valved line 55. Line 55 connects with the lower portion of a fractionating column 55 for introduction of the vaporsV thereinto. Preferably the iiashing of the cracked products from the heaters and reaction chamber in flash chamber 52 is controlled to effect the production of vapors containing products boiling above 650 to 800 F., at a pressure of from atmospheric, or even subatmospheric, to a pressure which is substantially above atmospheric but below the pressure in the reaction chamber, whereby constituents of heavy gas oil are contained therein. As already discussed hereinabove, the presence of the large number of moles of light products in the cracked products makes it possibleto remove more com-- pletely the lighter constituents therefrom in the vapors.

The operations of reaction chamber 49 and flash chamber 52 may be carried out in a single vessel, if desired, with slight modifications, for example, the mixed heated products in line l1 may be fed into a vessel similar to reaction chamber 49 by means of an open-end pipe which extends from the top or side thereof into the vessel and to a point in the Vertical axis thereof, with the open end disposed in the lower half of the vessel. The vessel will be provided with a bottom outlet (such as 54 in chamber 52) for the withdrawal of heavy residue and with atop outlet (such as 55 in chamber 52) for the withdrawal cf vaporous products. By maintaining a suitable level of heavy oil in the bottom of the vessel (and/or recycling a portion thereof as gasscrubber to a high point in the vessel) the temperature of the heavy oil in the bottom may be maintained as high as possible without obtaining undesirable cooking and the time period for maintaining the vaporous mixture under conversion conditions may be independently adjusted as desired. The process may be operated in a somewhat similar manner if it is desired to produce coke. The principal difference being that the temperature of operation is increased as much as possible and the heavy oil residue to be withdrawn from the bottom of the reaction chamber is eliminated. The production of coke by this method has an advantageously low con'- tent of volatile material on account of the unusually high temperature at which it is produced in the reaction chamber.

The separated vapors of the cracked products are introduced into the fractionator 56 so as to be intimately contacted therein with reduced crude oil (residual oil) taken from the bottom of tower I1. The reduced crude is fed by means of line 132, pump 51 therein, and then by either or4 both of parallel valved lines 59 and 50 to the lower portion of the fractionator 55. Fractionator 55 may be provided with suitable heating means, such as a heating coil 6|, placed inv the'- bottom portion thereof, and is also provided with suitable cooling means, such as a cooling coil 6E,- placed in the top portion thereof. The fractionating column is also provided with suitable trapout plates therein 64, 65, and 56 and with suitable outlet means for the withdrawal of gaseous overhead material and liquid residual material as well as any desired condensate cuts formed'by the condensation of the various normally liquid hydrocarbons in the cracked product. The overhead gaseous product is at least partially condensed in condenser 61 and collected in a storage vessel '69, from which the non-condensed lighter hydrocarbons may be vented or withdrawn through a valved line Til, a portion of the condensed product may be returned through a line 1l to the top of the fractionator 56 as a reflux, 4and the remainder of the condensed product may be withdrawn through a valved line 12. The lighter naphtha (gasoline) fraction is withdrawn from trap-out tray 64 through line 14 and delivered thereby to a suitable storage vessel 15. The heavier naphtha (300-400 F.) condensate cut of improved antiknock properties is withdrawn from trap-out tray S5 by means of a line 16 and delivered thereby to a suitable storage vessel 'il'.

The fractionating column 56 is operated in such a manner as to produce a light cracked oil fraction which is substantially free of straight run hydrocarbons and therefore is of sufficiently high refractoriness as to be advantageously treated with the straight. run heavy naphtha from the feed charge in the light oil heater and reformer il withoutthe deleterious formation of coke therein. In order to accomplish this, the operation of fractionator 5S must be coordinated with that of fractionator l1. Thus, fractionator i1 should be operated to remove in the more volatile fractions all straight run material boiling below about 500 F. and thus to produce a reduced crude bottoms fraction such as that when it is countercurfrently contacted with the cracked products in the lower portion of fractionator 55, there will be no appreciable proportion of straight run material :of .itheustove l oil "boiling :range present :which `is fseparated'in :thelight cracked oil fraction of cor At the same time it is` responding"boilingarange. desired .that the residual oil withdrawn from the rbottom-of fractionator 56 iwillcontain all of the 'straight .run .material which boils at v600" F. or higher and alsoheavier portions of cracked prod :.ucts removed from the flash chamber inthe vapor products.

lThe fractionator 56 is Voperated under conditions so that the bottoms residual product is `at a temperature rof'from about600 to 800 F. and usually at leastfrom 25 to .200" F.`higher 'than fthe temperature of the reduced crude as `with-- drawn from the fractionator I'I. The pressure maintained in the Yfractionator `56 4may be sad justed as desired,'but, becauseof'the presence oli relatively volatile hydrocarbons inthe cracked productait has beenfound preferable to operate under `a :pressure-which is substantially above atmospheric pressurerforrexample rfrom about 25 A.to about 150 p. s. i..a.

The heavy residual oil Awithdrawn `from the bottom of Afractionator 56 through line 19, which is providedwith `a suitable valve 80 and a pump 8 I is delivered thereby `to the-coil in heater 44"for treatment as 'already described ,hereinbefore. The residual oil in line 'I9 may be admixed, if desired, with a portion of thereduced crude in line 42 by means `of by-pass line82 and pump 8e placed therein. Whenithe process is iirst being: placed in operation only reduced crude 'taken from tower II may `be directed to and passed through heater 44. As the operation proceeds,

the Areduced crude may `then be gradually re placed by residual oil taken from `the bottom of *fractionator 5B. Any combinations of various proportions .of the two residual oils may be employed depending on ithe -particular 4requirements of a given system.

Any part or all of the light cracked `oil fraction (intermediate fraction) boiling between the endboiling point of the desired Icracked naphtha fraction (gasoline of high antiknock value) and the lowest `boiling point Aof the heavy oil (residual oil) is withdrawn vfrom trap-out tray 66 through a line 85,1which is'provided with a pump 8G and is delivered thereby to'line 39 wherein it is admixed with straight run fnaphtha and therewith delivered to the light oil heater and reformer 4l,

wherein the intermediate cracked oil is subjected to `cracking and reforming treatment'for the conversionl thereof `to, more valuable lighter products. If itis not desired to recycle all of the intermediate cracked condensate, either because of limitationsplaced onthe` process by physical limitations ofthe apparatus, or because of a demand for a portion of the product to lbe used as such or Ain some other operation, or for other reasons, a portion of this cracked fraction may be transferred, as by means `oia line 8l, to a suitable storage .vessel B-S. Also, in the practice `of the invention, it may b-e 'found to be desirable to utilize as feed to the light oil heater only intermediate cracked condensate if the amount formed inthe process is suiiicient for the purposes. This represents a particularly desirable method oi operating the process of the invention when the available charge stocks to behandled are largely heavy crude and/or even reduced crudes obtained ifromother operations andwherein the amount of straight run heavy naphtha `fraction which is available is of a very limited nature. In that case, after starting-up o'f the operations by the ansa-ers 10 rstfcrackingof the heavy oilby the processor the invention the straight run heavy naphtha may be gradually replaced by an intermediate cracked light oil fraction produced in the process `untilzonlysaid intermediate fraction is being sub- J'ected totheheat treatment and reforming conditions inthe light oil heater or reformer 4I. lAlso, when the available charge stocks are largely straight run reduced crude and a 1elativelysmall `proportion of crudeoil, such that when theltwo are combined in suitable proportions` or proportions 4which represent the ratio of their 'availabilities and then the ratio of straight runlight oil fraction of va stove oil range (40G-600 Fi) available therein to intermediate crackedfoil fractionfofrsimilar boiling range. produced in a cycle `of the operation of the process ofthe invention, `then an advantageous -embodiment of the invention is'.f one in Awhich a sel :ct'ed mixture of `straight run reduced-crude and crude oil, `after theprocess isbn-stream, is fed directly to the lower-*part `oi' the fractionator 56. Thus, the straight 'runref duced crude from a fractionator Il `mayfbeadmixed Awith a `suitable proportion of crude `foil taken from line I5,` if desired/by` means of a -v-alved line ifand the admixture delivered by means fo'f linesr42, 5S :andr and pumps "5l to the fractionatorf'. 'Inthis embodiment of the' invention it is lpreferredl'to -select the: operating conditions so i that the `intermediate cracked fraction 'which is` directedutoithe reforming heater'does-not contain more 'than about ten 'per cent of straight run material. The'presence of as much agitan per cent oifstraight run material `of Ythisintermediate temperature range inthe material frecycled to heater :4I .is :not detrimental, because of its dilution with fthek more vreiract'ory substances. :Howeveryon account of the non-.linearity of itherrelationshipltinvolved between refractoriness :of @the recycle Ymixture and `proportion of .straight V.run.hydrocarbons of the .indicated boiling range'therie'in, the presence offmore than about tenuper'. cent of. such straight run fmaterial resultszinirapidly risingffdeleterious cokingrin the crackingcoil.

"Other :means `nctshown may `be provided vfor withdrawing from the system any desired iportion `of` rany fuel oil, reduced crude, heavy :gas oil,;'lightfgas oil tor heavy rnaphtha fortreatfor use relsewhere, itrbeinglunder'stood that the `proportions oftheseintermediate productsvemployed in rthe;systemfforurther itreatment may be` regulated asfdcsiredfornecessary to'effect controLof the` operation foi `the :process Aof the invention.

It tis-to :befundersteod that theinvention-isnot to i'be limited byithe :fact that the means for collection-and withdrawal Aof the 'various A`inter-- mediate rproducts: is.` limited to` means for conveying them-fior further .treatment in the system sinc'ethe drawinghasmbeen limited to theaillustration of `sucl'l means'in `the 'interests .ossimplicity of presc-:ntationrolf the vsubject matter of the invention.

Towers or fractiona'tors II Iand `56- and 'also flash chamberlf; if itis desired, ,aresuitably provided `with trays, bubble caps and other suitable ,-gas and 'liquid vcontact?.means to 'eii'ect'ithe evaporation, i stripping, "condensation and absorption incidental to the `desired fractionation of the vapors passing therethrough. ".Reacti'on chambers 69 Jand '45a "are provided `with suitable auxiliary feed linies'anddischarge linesrprovided with the 'required' 'control `valves andthe` like -for blowing air *or oxygen `through ythem toueiiect use 'of-'straight `run heavy naphtha to effect the 25 oxidationandrremoval.of any cokeiformed theree ll in when it is desired to decoke by burning, or with other suitable removable closure mean-s when mechanical removal of coke is desired.

The cracking' of the heavy fraction (reduced crude) from the distillation of crude oil by first heating said heavy fraction to a cracking temperature but below the temperature at which any appreciable amount of coking occurs and then mixing the thus heated heavy fraction with a suitable heavy naphtha fraction which has been heated to a still higher temperature, which higher temperature is a reforming temperature for said naphtha fraction and at whichv temperature said heavy fraction would be subjected to coking if heated directly thereto, eifects a transfer of at least a portion of the sensible heat-,of the heated naphtha fraction to heat the heavy fraction to a temperature intermediate ofthe two first-men tioned temperatures whereby y the heavy fraction is converted still further tomre desirable products without the formation of any substantial amount of deleterious coke.

In order to illustrate the method of practicing the invention, without in any way limiting the invention thereby, the essentials of a preferred embodiment of the invention are described with reference to the accompanying drawing. A crude oil of a gravity of about 30 A. P. I. is fractionated in a fractionator such as I1 to produce a naphtha fraction (300-400 F., about 45 A. P. I.) and a reduced crude bottoms fraction (600 F. and up, about A. P. I.) and these two sepe arated fractions are processed in accordance with the invention as described hereinbefore and an intermediatecracked fraction of about A. P. I. is formed and separated fin the process and is recycled to the light oil heater 4I. Fractionator 56 is operated at a top temperature of about 350 F. and a bottom temperature of about 700 F., and under a pressure of about 90 p. s. i. a. A heavy oil residue is withdrawn from the bottom of the fractionator at the bottoms temperature of about 700 F. and fed to the coil of heater 44 wherein it is heated to a temperature of about 905 F. at a pressure of about 330 p. s. i. a. At the same time an intermediate cracked fraction having a boiling range of the order of 450 to 550 F. is withdrawn from fractionator 56 and fed to the heating coil of heater di wherein it is heated to a temperature of about 1050 to l100 F. at a pressure of about 330 p. s. i. a. The ratio of the heavy oil and the light oil heated in the heaters 44 and 4i, re-V spectively, is from about one to one to about two to one by volume. Upon mixing the products from the two heaters the temperature of the mixture is of the order of about 950 to 1000 F. and, after passing through the reaction chamber 49, with heat loss due to reaction, radiation, etc., the mixture is withdrawn at a temperature of about 915 F. The admixture is then flashed to a pressure of about 100 p. s. i. a. and a temperature of about 830 F. with the separation in flash chamber 52 of a heavy residue which is withdrawn from the bottom thereof at a temperature of 830 F. and of vaporous overhead withdrawn therefrom at a temperature of about 820 F. The overhead is then subjected to fractionation in fractionator 56, as described above.

I claim as my invention:

1. A thermal process of conversion of a low octane number naphtha cut to give a higher octane number product simultaneously with deep cracking of a heavy oil cut, which process corn-A prises: heating a low octane number straight run naphtha cut having an end boiling point of about 400 F. to a cracking and reforming temperature therefor of from about 1050 to 1100. F. at a pressure of about 330 p. s. i. a. while separately and simultaneously heating a petroleum residual heavy oil cut having an initial boiling point of at least about 600 F. to a lower cracking temperature therefor of about 905 F. at a pressure of about 330 p. si .i a. for a time insuicient to cause appreciable coking thereof; combining the thus heated naphtha products and the thus heated heavy oil in the ratio of from about 1:1 to about 2:1 of heavy oil to light oil and passing the combined products withoutY further addition of heat thereto from an external source through a reaction zone of enlarged cross-section and thereby effecting deeper cracking and conversion of the heavy oil by raising the temperature thereof by excess of sensible heat in the heated naphtha products; separating a vaporous product having a wide boiling range from the reaction zone; fractionating the separated vaporous product into a plurality of fractions comprising a high octane number gaso line naphtha fraction, a residual heavy oil fraction having an initial boiling point of at least about 600 F. and a light cracked oil fraction of intermediate boiling range of from about 450 to 550 F. and substantially free from straight run petroleum hydrocarbons boiling l'within the saine boiling range; recycling at least a substantial portion of said light cracked oil frac tion to the rst-mentioned reforming zone for ,further treatment therein under conditions the same as those in the first above-described crack ing and reforming temperature operation; and .recycling at least a substantial portion of said heavy oil fraction to the rst-mentioned cracking zone for further treatment therein under conditions similar to those used in the previous operation.

2. A thermal process of conversion of a low octane number naphtha cut tofgive a higher octane number product simultaneously with deep cracking of a heavy oil out, which process comprises: heating a low octane number Vstraight run naphtha cut having an end boiling po-int of about 400 F. to a cracking and reforming temperature therefor of from about 900 to 1100'J F. at a pressure of from to 1000 pounds per square inch adapted to effect cracking of the naphtha and conversion thereof with the production. of a revformed naphtha having improvedV antiknock properties and simultaneously heating a petro leum residual heavy oil cut having an initial boiling point of atleast about 600 F. to milder cracking conditions therefor of a temperaturey of from about 850 to 975 F. at a pressure of from about 100 to 1000 pounds per square inch, the temperature being selected to be lower than the temperature to which the naphtha cut is heated, for a time adapted to effect a maximum of cracking and conversion of the heavy oil without causing appreciable coking thereof; combining the thus heated naphtha products and the thus heated heavy oil'in the ratio of from about 1:1 to about 2:1 of heavy oil to light oil and passing the com bined products without further addition of heat thereto from an external source through a reaction zone of enlarged cross-section and thereby eiecting deeper cracking and conversion of the heavy oil by raising the temperature thereof by excess of sensible heat in the heated naphtha products; separating a vaporous produc-t having a wideboiling range from the reaction zone; fractionating the separated vaporous product into a plurality of fractions comprising a high octane number gasoline naphtha fraction, a residual heavy oil fraction having an initial boiling point of at least about 600 F. and a light cracked oil fraction of intermediate boiling range Within the range of from about 400 to 600 F. and substantially free from straight run petroleum hydrocarbons boiling within the same range; recycling at least a substantial portion of said light cracked oil fraction to the first-mentioned reforming zone for further' treatment therein under conditions the same as those in the rlrst above-described lcracking and reforming temperature operation; and recycling at least a substantial portion of said heavy oil fraction to the first-mentioned cracking zone for further treatment thereinunder conditions similar to those used in the previous operation.

3. A thermal process of converting a heavy oil fraction of the character of a straight run reduced 4crude to lighter hydrocarbons of high antiknock Value, which process comprises: heating a light `cracked oil fraction having a boiling range Within the range of from about 400 to 600 F., and being substantially free from straight run petroleum hydrocarbons boiling Within the same boiling range, to a cracking and reforming temperature therefor of from about 900 to 1100o F. at a pressure of from 100 to 1000 pounds per square inch adapted to eiect cracking of the cracked oil and conversion thereof with the production of a gasoline naphtha product having high octane value and simultaneously heating a petroleum residual heavy oil cut having an initial boiling point of at least about 600 F. to milder cracking conditions therefor of a temperature of from about 850 to 975 F. at a pressure of from about 100 to 1000 pounds per square inch, the temperature being selected to be lower than the temperature to which the cracked oil fraction is heated, for a time adapted to effect a maximum of cracking and conversion of the heavy oil without causing appreciable coking thereof; combining the thus heated cracked oil fraction and the thus heated heavy oil in the ratio of from about p reduced crude and of a minor proportion of a heavy crude oil and separating from said fractionating zone a plurality of fractions including a high octane number gasoline naphtha fraction, a second heavy oil fraction of similar initial boiling point as that of the first above-mentioned heavy oil fraction and a light cracked oil fraction of intermediate boiling range within the range of from about 400 to 600 F. and also containing not more than ten per cent by volume of straight run hydrocarbons; recycling at least a substantial portion of said separated light cracked oil fraction to the first-mentioned reforming Zone for further treatment therein under conditions the same as those in the First abovedescribed cracking and reforming temperature operation; and recycling at least a substantial portion of said heavy oil fraction to the first-mentioned cracking zone for further treatment therein under conditions similar to those used in the previous operation.

ROBERT BARTLETT EWELL.

REFERENCES CITED The following references are of record in the le of this patent:

UNITED STATES PATENTS Number Name Date 2,167,507 Heid July 25,. 1939 2,177,829 Huff Oct. 31, 1939 2,237,432 Huff Apr. 8,` 1941 2,296,601 Dorsett Sept. 22, 1942 

1. A THERMAL PROCESS OF CONVERSION OF A LOW OCTANE NUMBER NAPHTHA CUT TO GIVE A HIGHER OCTANE NUMBER PRODUCT SIMULTANEOUSLY WITH DEEP CRACKING OF A HEAVY OIL CUT, WHICH PROCESS COMPRISES: HEATING A LOW OCTANE NUMBER STRAIGHT RUN NAPHTHA CUT HAVING AN END BOILING POINT OF ABOUT 400*F. TO A CRACKING AND REFORMING TEMPERATURE THEREFOR OF FROM ABOUT 1050* TO 1100* F. AT A PRESSURE OF ABOUT 330 P.S.I.A. WHILE SEPARATELY AND SIMULTANEOUSLY HEATING A PETROLEUM RESIDUAL HEAVY OIL CUT HAVING AN INITIAL BOILING POINT OF AT LEAST ABOUT 600*F. TO A LOWER CRACKING TEMPERATURE THEREFOR OF ABOUT 905*F. AT A PRESSURE OF ABOUT 330 P.SI .I A. FOR A TIME INSUFFICIENT TO CAUSE APPRECIABLE COKING THEREOF; CONBINING THE THUS HEATED NAPHTHA PRODUCTS AND THE THUS HEATED HEAVY OIL IN THE RATIO OF FROM ABOUT 1:1 TO ABOUT 2:1 OF HEAVY OIL TO LIGHT OIL AND PASSING THE COMBINED PRODUCTS WITHOUT FURTHER ADDITION OF HEAT THERETO FROM AN EXTERNAL SOURCE THROUGH A REACTION ZONE OF ENLARGED CROSS-SECTION AND THEREBY EFFECTING DEEPER CRACKING AND CONVERSION OF THE HEAVY OIL BY RAISING THE TEMPERATURE THEREOF BY EXCESS OF SENSIBLE HEAT IN THE HEATED NAPHTHA PRODUCTS; SEPARAT- 